The present invention relates to an in-furnace level meter for measuring levels of in-furnace slag, melt, raw material, etc. in a convertor or the like by utilizing a microwave, and relates to an antenna for use in the in-furnace level meter.
In a conventional in-furnace level meter, for example, a microwave radar is provided at a furnace top of a convertor so that electromagnetic wave transmitted by the microwave radar through a waveguide and a transmission antenna is reflected on a slag surface. The electromagnetic wave thus reflected is received through a reception antenna and a waveguide and then subjected to signal processing to measure the distance between the microwave radar and the in-furnace slag surface.
As the microwave radar for use for such measurement, there are various kinds of measurement systems as follows:
One of those systems is, for example, an FM-CW microwave radar system. As disclosed in Japanese Patent Laid-Open Publication No. 63-21584 this measurement system comprises the steps of: transmitting a microwave formed by frequency-modulating a continuous microwave of about 10 GHz, from an antenna toward a level surface; and counting a beat frequency produced by mixing the transmission signal with the wave reflected on the level surface to thereby measure the distance between the microwave radar and the level surface. That is, the distance measurement in this measuring system is based on the fact that the propagation time of the microwave required for reciprocating the distance between the antenna and the level surface corresponds to the aforementioned beat frequency.
Another measurement system is a pulse-modulated microwave radar system. This measurement system comprises the steps of: pulse-modulating a microwave having a frequency of about 10 GHz to about 20 GHz and transmitting the pulse-modulated microwave as in an ordinary airplane radar; and measuring distance between the radar and the level surface on the basis of the fact that the propagation time of the microwave required for receiving the microwave reflected on the level surface is proportional to the distance between the radar and the level surface.
In the conventional in-furnace level meter using such a microwave radar, the transmission antenna and the reception antenna are fixed to specific positions at the furnace top portion of the convertor or in the furnace. Accordingly, there arise the following problems as to the change of the slag level in the furnace.
In the case where the transmission and reception antennas are fixed at the furnace top portion, the slag level position cannot be often measured accurately because of the influence of unnecessary signals reflected from the in-furnace lance, the furnace opening portion and the furnace wall portion when the distance between the transmission and reception antennas and the slag level increases as the slag level in the furnace decreases.
In the case where the transmission and reception antennas are fixed at the deep portion inside the furnace, the slag level position cannot be often measured accurately because of occurrence of signal attenuation, blockade of the transmission and reception antennas, etc. caused by the deposition of scattered slag, ground metal, dust, etc. on the transmission and reception antennas when the distance between the transmission and reception antennas and the slag level decreases as the slag level in the furnace increases.